Faults and folds in the Miri Formation, Sarawak

Recent geological studies carried out in the Miri Formation reveals several structural elements and stratigraphic patterns that warrant further description of the Formation. Particularly the existence of outcrops that shows a very big contrast of a thick vertically dipping section with a sub-horizontal or gently dipping sequence situated side by side. Due to sudden change on bedding orientation and topography, it was interpreted by Schumacher (1941) and Shuib (2003) as thrust fault called the Canada Hill Thrust. Schumacher in 1941 developed a structural model of Miri with the following elements: (i) a set of steep normal faults hading to the northwest with a vertical displacement of thousands of feet; (ii) a set of flat normal faults, hading to the southeast; (iii) a set of merging reverse faults, hading to the northwest (the Canada Hill Thrust); and (iv) an asymmetric, slightly overturned, anticlinal fold. Locally the formation was too competent to buckle thus it broke and creating the thrust faults such as the Canada Hill thrust fault at the back of the Hill (Berbeito, 2003). However, the high angle fault plane (± 55o) separating the two contrasting blocks is not likely to be the feature of a thrust fault (Spencer, 1988). The absence of a drag fold in the field and the presence of a very short contact zone for a very big contrast between a thick sequence of vertically dipping section with a sub-horizontal or gently dipping sequence situated side by side suggests there is a serious weakness in the structural model that was proposed by Schumacher in1941.